WASHINGTON — The alleged mastermind of the 9/11 attacks and four codefendents being held at the US military's Guantánamo Bay detention center in Cuba appear to be trying to seize control of their own fates – even if that brings the day of their possible executions closer.

Khalid Sheikh Mohammed told a military judge on Monday that he and his fellows wished to immediately confess at their war-crimes tribunal, setting up likely guilty pleas and impositions of the death penalty.

It's not clear whether the five Guantánamo detainees will immediately get their stated wish. The judge in the proceedings, Army Col. Stephen Henley, said two of them cannot file pleas until the military determines whether they are mentally competent. Mr. Mohammed and the remaining defendants then said they would wait, so they could all plead together.

But at the least the defendants' surprise move is another blow to the Bush administration's teetering tribunal system. After all the evidence of harsh treatment the US has meted out to war-on-terror detainees, the Guantánamo proceedings shouldn't give the impression that the tribunals are eagerly accepting applications for martyrdom, says one expert.

Mohammed has already told US interrogators that he was the person who pushed for and planned the attacks of Sept. 11, 2001. At his Dec. 8 appearance, he said he has no faith in the judge, his lawyers, or President Bush.

"I don't trust you," he said in English to the tribunal.

Mohammed and his fellow defendants said they decided on Nov. 4, the day of President-elect Obama's electoral victory, to abandon all defense against the capital charges facing them.

Mr. Obama opposes the military commission system and has said he will close the Guantánamo Bay detention camp soon after taking office.

The commissions have won three convictions. But they have been criticized for allowing statements obtained through harsh interrogations and for allowing hearsay to be introduced as evidence. The government has acknowledged that Mohammed's interrogations included waterboarding, a form of simulated drowning that many consider to be torture.

In one sense, it is not surprising that prisoners kept under such circumstances should decide in essence to refuse to recognize the court at all.

"Some would say this is what happens after five years of, let's say, extremely harsh treatment," says Mr. Hannum.

But given that the defendants are admitted terrorists, neither is it surprising that they would not shun, and even embrace, the possibility of the death penalty. After all, at one time they embraced the possibility of suicide attacks.

"There's no reason why they wouldn't be willing to be executed," says Hannum.